(1) Field of the Invention
The present invention relates to a method of fertile breeding control in female bovines by means of overlapping dosages of a progestin and a luteolytic agent using an implant for releasing low levels of the progestin over a time period into the blood stream and injection of the luteolytic agent towards the end of the period so that the progestin and agent are being administered together. In particular the present invention relates to the use of a vaginal implant for releasing the progestin over a period of time into the blood stream.
(2) Prior Art
Success of detecting cows in estrus averages 50 percent but 85 to 100 percent is possible. High success in detecting estrus requires at least four 30 minute periods of observation or 2 hours per day. Thus, low success of detecting estrus is due largely to inadequate observations of cows because labor is expensive and/or not available. Failure to observe for or detect estrus limits use and success of artificial insemination (AI). Presently AI is used on about 75 percent of dairy cattle and about 5 percent of beef cattle. Development of methods to predict estrus or ovulation would not be fruitful since this approach only addresses one animal and requires labor and management. In addition, no profound biological parameter has been identified to form a basis for a "cow-side" test of estrus/ovulation.
Methods exists to control when estrus and/or ovulation occur. Commercially available methods include:
a. Syncro-Mate B.RTM. from CEVA (a French company)
b. Prostaglandin F.sub.2 alpha and analogs
(1) Lutalyse.RTM. from Upjohn PA1 (2) Estrumate.RTM. from Haver Lockhardt PA1 (3) Syncro-Cept.RTM. from Diamond Labs.
The value of the present methods (listed above) to control estrus and/or ovulation is realized primarily through improved success of detecting estrus. However the ultimate goal of controlling ovulation is for AI to occur at a prescribed time after application of agents to control ovulation (AI by appointment) without regard for estrus. Acceptable results with "AI by appointment" will only be realized if all cattle in a group ovulate within a range of 24 hours. Present methods to control ovulation do not cause sufficient precision to warrant AI by appointment. For example, with prostaglandins, the range for occurrence of estrus or ovulation is 4 to 5 days. With Syncro-Mate B the range is 3 to 4 days. In addition to variation among individuals within a group, average intervals to estrus or ovulation are highly variable among groups of cattle, particularly when using prostaglandin.
U.S. Pat. No. 3,892,855 to Short describes the closest known prior art which uses a progestin and a luteolytic agent. In the method described in this patent, a subcutaneous progestin implant is removed at the time of injection of the luteolytic agent. The result is the onset of estrus and ovulation over a period of 1 to 5 days which is a wide time span. Further subcutaneous implants produce a risk of infection.